Place 3 or so cups of water in a saucepan and bring to the boil on high heat. Add potato slices and cook for 5 minutes or until slices have softened but are still firm enough to stay in one piece. Drain and allow to cool.

Once cooled enough to handle arrange in layers over the filling, starting on the outside and working in. Brush potatoes with the skim milk.

Place the casserole in the oven and bake for 1 hour or until potatoes are golden on top and soft.